1. Field of the Invention
This invention pertains in general to a system for remediation of biological waste, and more particularly to a system for remediation of livestock waste through aerobic and anaerobic bacterial digestion.
2. Description of the Related Art
As the global population increases there is a corresponding need to increase food production. Large scale food production operations such as concentrated animal feeding operations (CAFOs) produce large volumes of livestock waste. Livestock waste can contain compounds such as manure, fertilizer compounds, hydrocarbons and antibiotics. Many of these compounds must be remediated in order to attenuate negative environmental impact caused by the compounds. Accordingly, efficient methods of livestock waste remediation are needed to support environmentally sustainable food production for a growing global population.
One popular method of livestock waste remediation is through the use of livestock waste lagoons. A livestock waste lagoon is a sealed tank into which liquid livestock waste is combined with water to create an effluent for remediation. Typically, the liquid livestock waste is combined with water collected from rainfall. Livestock waste lagoons act as “digesters” in which anaerobic or aerobic bacteria decompose the compounds in the effluent into gases, liquids and sludge, thus remediating the compounds. Anaerobic bacteria are bacteria which do not survive in the presence of free oxygen. Aerobic bacteria require free elemental (dissolved) oxygen for survival.
Anaerobic lagoons are most commonly used for livestock waste treatment. Anaerobic bacteria can decompose or “digest” more organic compounds per unit lagoon volume than aerobic bacteria and are predominantly used for treatment of concentrated organic waste. Since anaerobic digestion is not dependent on dissolved oxygen, lagoons can be much deeper and require less surface area, thus enabling a greater volume of waste to be remediated. However, anaerobic digestion results in the production and emission of noxious gases, primarily hydrogen sulfide, ammonia, and intermediate organic acids.
Aerobic lagoons remediate livestock waste through digestion of the waste by aerobic bacteria. The main advantage of aerobic lagoons is that aerobic digestion of livestock waste tends to more thoroughly remediate organic compounds present in effluent than anaerobic digestion. Aerobic digestion of livestock waste also produces relatively odor-free end products.
In aerobic lagoons, oxygen diffusion occurs across the surface of the lagoon resulting in an increased dissolved oxygen concentration which enables the proliferation of aerobic bacteria. Because of the need for an increased dissolved oxygen concentration, naturally aerobic lagoons are designed on the basis of surface area rather than volume. Water depths of aerobic lagoons are typically shallow, ranging from 3 to 5 feet. Consequently, large amounts of land are required for naturally aerobic lagoons—as much as 25 times more surface area and 10 times more volume than an anaerobic lagoon 10 feet deep. Thus, naturally aerobic lagoons are impractical and are generally not used for livestock waste remediation. To compensate for lack of surface area, some aerobic lagoons are mechanically aerated.
Double-stage lagoons provide one method of combining the benefits of aerobic digestion and anaerobic digestion of livestock waste. In double stage lagoons, incoming waste is first input to an anaerobic first-stage lagoon. Overflow from the anaerobic first-stage lagoon is output to an aerobic second-stage lagoon. This produces an effluent end product that has less odor and fewer organic solids than anaerobic digestion alone. However, double-stage lagoons require the maintenance of two separate lagoons and their respective bacterial populations. Further, the anaerobic first-stage lagoon still produces noxious gases.
Accordingly, there is a need for systems which maximize both the efficiency of remediation and completeness of remediation. There is an additional need for systems which utilize the by-products of remediation.